Liquid fuel burner with rotatable atomizing cup



June 21, 1949. H. K. J. VAN DEN BUSSCHE 2,474,020

LIQUID FUEL BURNER WITH ROTATABLE ATOMIZING CUP Filed June 11, 1947 kill-ll... lQlr ovl llll E I I I r11 ll-H HWQTWQP: HendPiK K.J.van Glen @ussahe his Mhszmag Patented June 21, 1949 LIQUID FUEL BURNER wrrn ROTATABLE aromzmo our Hendrik K. J. van 'den Bussche, Delft, Netherlands, assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application June 11, 1947, Serial No. 753,845 In the Netherlands June 25, 1946 This invention relates to the combustion of liquid fuel which is fed into a rapidly'rotating atomlzlng cup which is flared forwardly, and from which the fuel is discharged into a surrounding stream of advancing air, being thereby atomized, i. e., broken up into minute droplets.

In many cases, particularly when burning thick, residual oil, there is a drawback to these burners in that solid particles, consisting of partially burnt fuel and ash settle on the inner wall of the cup, especially on the portion having the lowest conicity. This fouling of the cup surface causes uneven distribution of the oil film on the cup wall and results in irregularities in the quantity of oil and the size of oil particles discharged at various portions of the cup edge. With uneven distribution the efiectiveness of the atomization and the efliciency of the combustion are adversely affected.

It is the principal object of this invention to provide an improved method of burning liquid fuel in a rotating atomizer cup burner, and to provide an improved rotating atomizer cup burner, wherein the fouling of the cup by deposition of sootppartially burnt fuel, ash and the like is obviated or greatly reduced.

It is a further object to provide an improved method and apparatus of the type "described wherein the vacuum normally occurring within the rotating cup in burners of this type is relieved by the admission of air into the interior of the cup. 1

Still a further object is to provide an improved burner wherein the tendency toward uneven flow of oil and deposition of extraneous matter is minimized by providing a smooth surface for the cup wall. i

The foregoing and other objects will become apparent from the following description. taken in connection with the drawing, the single figure of which is a longitudinal sectional view of an improved burner constructed in accordance with the invention. V

In burners of the rotating atomizer cup type, wherein the oil is-discharged from the edge of a flared cup into a surrounding current of advancing air, it is necessary that the ,oil to be atomized leave the edge of the cup as a ver thin film. In tests leading up .to the present invention it was found that the oil, upon reaching the cup edge, appears to break up andv form streaks of oil along the cup edge. These streaks contracted to form torus-shaped columns of liquid. These-columns, which extend from the cup edge at regular intervals, are unstable and break up into droplets 4 Claims. (Cl. 15877) 2 at a short distance from the cup. Since the size of the resulting droplets should, for good atomization, be as small as possible from the start,

'i. e., before being further subdivided by the air current, it is essential to keep the torus-columns small. When the distribution of the oil over the ization results.

It was, further, found that the flow of oil as a thin film on the face of'the cup is greatly influenced by very slight irregularities, and that a particle of soot or the like at a point some distance back from the cup edge adversely affects the flow of the oil at the cup edge. Moreover, irregularities in the structure of the cup wall itself may result in irregular distribution of the flow-of oil. Such misdistribution was, moveover, found to be conducive. to the deposition of partially' burnt fuel, soot or ash, which aggravates the uneven distribution of oil. a

Since the oil is, in such burners, fed by centrifugal force caused by the rotation of the cup, it was heretofore considered desirable to make the interior wall of the cup only moderately smooth, leaving suflicient roughness to insure ro tation of the oil with the cup wall. It was further found that sooting and fouling is caused by solid particles which are carried back into the cup from the combustion zone by a. vortex action which originates within the hollow flame and hurls the particles onto the wall of the cup.

atomization and more efficient combustion are attained by two expedients which may be applied separately or, preferably, jointly: The first is concerned with reducing backwardfiow into the cup of such small particles; the other isconcerned with reducing the tendency of such particles as enter the cup to adhere to the cup wall. The former expedient involves insuring that the vortex center of the flamedoesnot approach too' closelygto the cup and this is effected by admitting a small quantity of auxiliary air into the cup.

The partial vacuum withinthe cup which other- I e. g., by polishing orby applying a coating. such' as a chromium plated finish. Solid particles were found to adhere less. readily to such a smooth surface, possibly for two reasons: They are'less effectively held by a smooth surface; and they are According to the present invention improved more likely to be prevented from reaching the wall and to be flushed away from there by the moving oil film if the oil is very evenly distributed as a result of the polished surface.

Referring to the drawing, I is a supporting housing having bearings 2 and 3 for rotatably mounting a hollow shaft 4. .The hollow shaft is generally cylindrical throughout but its bore is tapered slightly, widening toward the head of the burner beginning slightly forwardly of the bearing 2. A pulley 5, mountedon shaft 4, may be driven by a belt, not shown, from any source of power for imparting a high rotational velocity to the shaft.

The atomizer cup 6 is rigidly mounted at the forward end of the shaft 4 by screw threads. The inner surface of the cup may have any smooth, continuous form, and is, preferably, in

the form shown, viz., conical in rear for the greater portion of its length, and curved outwardly in the form of a calyx at its forward part, terminating in a sharp knife edge I. To minimize the deposition of solids on the cup wall it is desirable to construct the cup so that the conicity is not less than 12 at any point extending back from the cup edge for a distance equal to at least 0.8 of the diameter at the edge. By conicity is meant the apex angle of the cup walls which should, according to this definition, diverge at least 6 from the cup axis. Thus, in the drawing, if the cup diameter is d, the conicity for the length e should not be less than 12, the length e being not less than 0.8d and, preferably, somewhat greater than-d, as shown. It was found that by selecting such a shape the component of the centrifugal force of the oil along the cup wall is sufficiently great to flush away many deposited particles. It is further desirable, for attaining good atomization, to flare the outer edge ofthe cup so that, at the outer edge, the tangent to the inner surface of the cup makes an angle of between 60 and 90 with the axis, although good results have been attained with smaller angles, down to about 30. This angle is 78 in the embodiment shown. The selection of such an angle at the discharge edge is not part of my invention. The inner surface of the cup is polished to provide a very smooth finish.

Liquid fuel, such as oil, is introduced into the hollow shaft 4 through a stationary supply pipe 8, closed at its forward end and mounted in a support 9, to extend concentrically with the shaft and connected to a source of fuel oil by flow control means not shown. Oil flows from the supply pipe through an orifice I0, directed laterally against the surface of the shaft 4. Packing means, such as wire rings, may be provided at H, but these may be omitted.

An air conduit I 2 is mounted by support 9 to extend forwardly through the pipe 8 and through the wall of the latter. This air conduit need not be connected to a source of air supply but will function by simply taking its air from the atmosp'here. It may be of small diameter. It is, of course, also possible to inject air under pressure through the conduit l2, but such air is auxiliary air and does not constitute a major part of the air required for combustion. It is desirable to feed the auxiliary air into the cup axially with respect thereto with a view to avoiding any disturbance to the even distribution and flow of 'oil :on its inner surface.

4 bounded on the inner side by a jacket l3 secured to the housing I, and on the outer side by an air nozzle I4 having its rear portion enlarged to form a whirl chamber l5. It is carried by the rear section of the whirl chamber housing IS. The latter is provided with one or more tangentially directed air inlet ports l'l, through which air may be supplied under pressure from any suitable source, such as a blower or fan, not shown. The air nozzle I4 may be slightly convergent toward its mouth. In the operation of the burner, oil is supplied to the supply pipe 8 at the desired rate and the hollow shaft 4, together with the cup, is rotated at a high speed, e. g., 3,000 to 23,000 rev. per min. The liquid oil impinges against the inner wall of the shaft 4 and is evenly distributed thereon; it

' advances toward the atomizing cup by centrifugal Air for combustion and atomization is supplied force, brought about by the conical shape of the bore and the rapid rotation. In the cup the film is thinned out at an increasing rate, the thinner being most rapid in the forward, calyx-shaped portion of the cup. The thin'film of oil is discharged from the sharp edge I as a fine mist. which is caught and atomized by the advancing air current. The resulting dispersion of fuel and air is ignited by any known means, such as an arc. The direction of rotation of the cup is preferably opposite to the direction of rotation imparted to the air by the tangential inlets i'l, whereby the oil is caught by the air at a greater relative velocity and a greater degree of atomization is effected. The burning and the rotation create .a vortex and a vacuum within the cup whichis relieved by auxiliary air admitted through the air conduit l2, thereby minimizing the carrying back of soot and the like. By this invention it is possible to maintain a burner in operation for a longer period of time without fouling than is possible with burners of conventional design.

I claim as my invention:

l. A burner for liquid fuel comprising a rotatable atomizing cup having a continuous highly polished inner surface widening toward the front, a tubular shaft secured to and extending rearwardly from said cup, means for rotating said shaft and cup at a high velocity, an oil supply pipe within said tubular shaft, closed at its forward end and provided with an orifice near said forward end, and an air supply conduit within said oil supply pipe having its intake in communication with the atmosphere outside of the burner and havin its discharge end forwardly of said oil supply pipe and substantially axially with respect to the atomizing cup.

2. A burner for liquid fuel comprising a rotatable atomizing cup having its inner surface widening toward the front and having a highly polished inner surface, and means for supplying liquid fuel into the cup.

'3. A burner for liquid fuel comprising a'supporting housing, a hollow shaft rotatably mounted therein, means for rotating said shaft at a high velocity, an atomizing cup mounted on the forward end of said hollow shaft in communication therewith and having :a continuous highly polished inner surface flaring toward the front, a tubular air nozzle surrounding said cup for supplying atomizing and combustion air in an annular stream, means for supplyin liquid fuel to said'hollow shaft, and an air supply conduit within said hollow shaft having its discharge end near the base of the atomizing cup for supplying auxiliary air-into the atomizing cup substantially axially with respect theret0..

4. A burner for liquid fuel comprising a rotat- 5 6 able atomizing cup having a continuous. smootgh REFERENCES CITED inner surface having a. high polish widening ward the front, means for rotating said cup at a a; g g g are of record in the high velocity, means for supplying liquid fuel into the atomizing cup, means for supplyin an annus UNITED STATES PATENTS hr, and forwardly moving stream of atomlzing Number Name we d co i a su oun i s t e cup. 1,733,413 Kay Oct 39, 1939 mm Busm- 1,739,548 mam Dec. 1'1, 192a 

